It is well-known that a wide variety of compounds containing carboxylic acid functions are biologically active. For example, such structure is characteristic of non-steroidal anti-inflammatory/non-narcotic analgesic agents such as indomethacin, aspirin, naproxen and the like; cephalosporin antibiotics, e.g. cefmetazole, cefazolin, cephalexin, etc.; penicillin antibiotics such as ampicillin, amoxicillin, hetacillin and the like; as well as other compounds having diverse biological properties and the structures.
Nevertheless, it is also well-known that such prior art compounds are characterized by certain inherent disadvantages, notably serious bioavailability and physiological availability problems upon administration. Such reduced availability is attributed in part to significant ionization of the carboxylic acid functional group at physiological pH, which results in the fact that such compounds are poorly absorbed through lipid-water membrane barriers and are irritating.
Thus, a clear need exists for new derivatives of the known bio-affecting acids which will be devoid of the disadvantages inherent in those prior art compounds.
A few compounds structurally related to certain compounds of formula (I) have been reported in the literature. Thus, U.S. Pat. No. 3,897,437 to Haas et al [Chemical Abstracts, 83, 178848j (1975)] describes selected substituted anilinophenylacetic acid (2,3 or 4-pyridyl)methyl esters having antiinflammatory, analgesic and uv absorption properties. See also Chemical Abstracts, 80, 146029q (1974) describing a smaller group of pyridylalkyl (2-anilinophenyl)acetates and disclosing the same properties. Pyridylalkyl .alpha.-(4-cycloalkenylphenyl)propionates, useful as inflammation inhibitors and analgesics, are described in Chemical Abstracts, 80, 146032k (1974). Chemical Abstracts, 79, 115415n (1973) describes yet another group of pyridylmethyl esters, which potentiate barbiturate narcosis, some of which are also reported as having analgesic, spasmolytic and antihistaminic activity. Yet other groups of pyridylmethyl esters are reported in Chemical Abstracts, 79, 31888f (1973) [no utility disclosed]; Chemical Abstracts, 80, 82432f (1974) [no utility disclosed]; Chemical Abstracts, 85, 78017k (1976) [said to affect blood cholesterol and blood lipids]; Chemical Abstracts, 85, 192401f (1976) [said to lower serum cholesterol and blood lipids]; and U.S. Pat. No. 4,184,040 [for treatment of atherosclerosis]. See also Camble et al, J. Chem. Soc. (C), 1969, 1911, which describes use of ##STR3## as a protecting group for amino acids in peptide synthesis. However, the compounds of the present invention are structurally distinct from the prior art compounds. Moreover, there is no suggestion in the literature that these compounds would be characterized by low pKa's, which result in enhanced stability and greater bioavailability as compared to their parent acids.